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A study on the stress ratio around welding lines of ribs in orthotropic steel decks
Published in Hiroshi Yokota, Dan M. Frangopol, Bridge Maintenance, Safety, Management, Life-Cycle Sustainability and Innovations, 2021
S. Kakizaki, H. Onishi, S. Ubagami, K. Hoshikawa, A. Horiai
A vibration fatigue tester developed at Nagoya University was used for the vibration fatigue test using the specimens. Figure 1 shows an overview of the vibration fatigue tester and a photo of the test situation, respectively. In specimen No.1 of this study, we carried out vibration fatigue test with the rib facing downward assuming actual bridges. However, the assumed cracks couldn’t be detected. The specimens were placed so that it faced upward. This test machine was designed to vibrate specimens by rotating an eccentric motor put in the cantilever and installed on the free end side, and generate a bending stress in the specimens. By changing the mounting position and the rotational speed of the eccentric motor, the magnitude of the stress generated in the specimens and the vibration frequency can be calibrated. In this time, the load magnitude was calibrated by calibrating the frequency so that the stress obtained from the strain obtained from the trial test in advance was the candidate nominal stress. In addition, only the rotational vibration of the motor results in a fatigue test in which the stress ratio was alternating (R=-1). In this test, a coil spring was installed at the tip of the specimen, and the specimen was pushed down by this coil spring. The fatigue test was carried out with the stress ratio applied to the specimen being pulsated (R> 0).
Component and Subsystem Reliability Testing
Published in Ali J Jamnia, Khaled Atua, Executing Design for Reliability within the Product Life Cycle, 2019
where T is the exposure time, S is the applied stress (i.e., acceleration), and n is the power law coefficient.10Edson (2018) suggests that for random vibration fatigue of solder, n = 4. We also need to keep in mind that random vibrations are applied only when the engine runs. For a primer on random vibration, see Jamnia (2016). In this test case, our assumption for random vibrations input is given in Table 8.9; however, data may need to be extracted either from other tests or standards. Briefly, we are suggesting that the ECM experiences four different levels of root mean square accelerations (Grms) during its 7-hour operation. For instance, in the travel sequence 1, the ECM is subjected to one hour of random vibration at Grms = 0.02. For a 364-day year, this means that the exposure to this stress level is 364 hours, and 3540 hours during a 10-year design life. Knowing this information, we can calculate the damage caused by this stress level during the design life: Damage=36400.024=0.001
A metal-oxide-semiconductor devices reliability assessing method based on physics of failure
Published in Stein Haugen, Anne Barros, Coen van Gulijk, Trond Kongsvik, Jan Erik Vinnem, Safety and Reliability – Safe Societies in a Changing World, 2018
Hantian Gu, Ming Zhu, Wei Zhang, Lei Zhang, Hengjing Zhu, Min Tang
In terms of mechanisms such as random vibration fatigue, CDRA is more appropriate to solve the problem of the cumulative damage. Here, considering the order and interaction effects of variable amplitude loading, the Corten-Dolan approach is determined to calculate the TTF of failure mechanisms. The formula is, () Ng=N1∑i=1mαi(σiσ1)d
Vibration fatigue analysis of high-speed railway vehicle carbody under shaking condition
Published in Vehicle System Dynamics, 2021
Fansong Li, Hao Wu, Chaotao Liu, Pingbo Wu, Jing Zeng
Vibration fatigue mainly studies the stress state and fatigue strength of the structure in resonance state when the external excitation frequency is the same or close to the frequency of natural mode [3], while the traditional fatigue mainly studies the case that the excitation frequency is far lower than the first natural mode frequency of the structure. As bearing structure has a lot of modes, it is difficult to accurately grasp the frequencies of external excitation from the environment in which the structure is located if there is not a large amount of environmental test data support in the early design stage, which may cause the structure to be in resonance state, and then lead to the occurrence of vibration fatigue problems. In addition, vibration fatigue analysis has two main differences. First, in post-processing of dynamic stress, the traditional statistical method of Rain Flow counting is abandoned and the stress statistics is carried out by the spectral method [4–6], which is used to improve the calculation efficiency. Second, in dynamic stress simulation, vibration fatigue needs to consider the modal parameters of the structure and the influence of structural dynamic characteristics on deformation [3,7], but traditional fatigue simulation mainly considers structural stiffness, that is, Hooke's law principle.